1. Field of the Invention
The present general inventive concept relates to an ink composition, an ink cartridge including the ink composition, and an inkjet recording apparatus including the ink cartridge, and more particularly, to an ink composition for inkjet recording which has characteristics to prevent formation of depositions therein over time in a thermal-type inkjet printer to obtain high storage stability and good ejection properties, an ink cartridge including the ink composition, and an inkjet recording apparatus including the ink cartridge.
2. Description of the Related Art
Inkjet recording can be performed with low noise and at high speed. As such, inkjet recording methods are attracting more and more attention. In inkjet printers, a highly flowable liquid is ejected from a thin nozzle to be recorded on a medium. Inkjet printers are categorized into on-demand ejection type inkjet printers and continuous ejection type inkjet printers.
An ink for high-speed inkjet printers should be able to be manipulated into ink droplets having a uniform size, and should be able to be ejected at a uniform speed and in a uniform direction through a nozzle. When inkjet recording is performed many times, a heater of a recording head may be destroyed and as such the ink cannot be ejected, or depositions can build up on the heater and thus thermal energy of the heat cannot be efficiently transferred. In addition, there is a need to reduce a number of cleaning processes required by preventing formation of depositions in nozzles. Furthermore, ink should be stably stored. If ink is unstably stored, ink injection is unstable and thus images to be formed can be skipped or recorded in a lower than desired concentration.
Japanese Patent Laid-open Publication No. hei 8-337747 relates to an aqueous ink having storage stability and ejection stability containing an inorganic sulfate that makes a polyvalent metal ion soluble in water. Specifically, ink ejection stability can be obtained in such a manner that a metal ion in the ink is captured by a sulfuric ion to prevent formation of a low-soluble complex due to coordination of the metal ion with an anion, such as a carboxylic acid induced from an additive.
As another method of obtaining ink stability, an impurity, such as a metal ion, generated when a dye is synthesized can be removed from the dye. However, even when an impurity, such as a metal ion, is removed by refining of the ink, depositions of the dye are generated because thermal decomposition of the dye in the ink cannot be avoided.
According to a method to improve a long-term storage stability of an aqueous ink, a chelating agent can be added to ink for inkjet recording to mask a metal ion in dye so that blockages in printing heads due to a metal ion can be prevented. In general, an ethylenediamine tetraacetic acid (EDTA) salt or the like are usually used as a chelating agent. When the concentration of such a chelating agent is high, a surface layer of a heater gradually corrodes and thus a thickness of the surface layer is reduced. Consequently, after a predetermined time period, the surface layer corrodes completely and the heater is short-circuited.
Accordingly, the techniques described above are not sufficient to completely prevent formation of depositions, and other known methods also have limited effects or side effects.